This work is focused on the synthesis and self-assembly of novel dendritic star polymers with a dendritic polyamidoamine core and many linear polystyrene arms. The polymers can synchronously form unimolecular micelles (ca. 10 nm) and large multimolecular micelles (ca. 100 nm) in selected solvents (tetrahydrofuran/methanol) at room temperature. Atomic force microscopy, scanning electron microscopy, and dynamic light scattering measurements have provided direct evidence that the large micelles are a kind of multimicelle aggregate with the basic building units of unimolecular micelles. Accordingly, a possible self-assembly process is put forward, and a new aggregate model, termed multimicelle aggregate, is suggested to explain the formation of the large micelles. In the multimicelle aggregate model, the large micelles are the aggregates of small micelles associated by intermicellar interactions such as hydrogen bonds and p-p stacking interactions. It is the first demonstration of the self-assembly mechanism for the large multimolecular micelles generated from the solution self-assembly of dendritic star polymers. (C) 2008 Wiley Periodicals, Inc.